add CSP to nginx config

Author: kmurphypolygon

.github/assets/nginx.conf

@@ -5,6 +5,8 @@ server {
 
     error_page 404 /404.html;
 
+    add_header Content-Security-Policy upgrade-insecure-requests;
+
     location / {
         try_files $uri.html $uri $uri/ =404;
     }